The subject application claims a priority under 35 U.S.C. xc2xa7119 on Chinese Patent Application No. 98113402.5, filed on Jan. 6, 1998, which is herein incorporated by reference.
The present invention relates to a solid laser, especially an alignment-free solid laser suitable for industry, military (national defence), medical and scientific research fields.
At present, most widely used solid lasers consist of an active laser material (also called laser rod), a pump system and an optical resonant cavity. After absorbing enough pump energy, the active material achieves population inversion and stimulated radiation is generated as a result. With the help of the optical cavity, the stimulated radiation oscillates and is amplified in the cavity, and an amplified stimulated coherent light beam, which is a laser beam of high intensity, is generated. Most cavities consist of two mirrors parallel to each other and the active material is located on the axis of the cavity. The two plane mirrors are required to be parallel to each other exactly and are perpendicular to the active material axis. When the angle between the two mirrors is larger than 20xe2x80x3 there will be no laser emission. Therefore, the laser must be designed to have two sets of special means for its regulation to meet the requirement for the cavity and needs to be regulated with the help of a special equipment, otherwise, the laser is impossible to be operated normally. Thus, the structure and the regulation of the optical resonant cavity of the laser have problems in installation, operation and maintenance. When the optical and cavity mirrors axes of the laser cavity deviate from their original position by an applied shock, hit or self-produced heat during the laser operation, the cavity can be in disalignment, even if it is regulated in alignment already. Once disalignment occurs, the output laser energy can be reduced, the beam quality can become inferior, and therefore the availability of the laser is affected. Even worse, the laser may have no output and become useless. Besides, the inhomogeneity and the heat-induced distortion of the active material make the laser beam inferior and the local excessive power density is likely to cause the damage of the laser material. These problems are unavoidable for the conventional laser cavity, because laser beam must oscillates back and forth along the same path. Therefore, forming an alignment-free resonant cavity (i.e. getting laser output after installation without alignment.) to improve its machinery and heat stability and beam quality is an important problem demanding prompt solution. Prior solid lasers require high alignment accuracy and alignment is difficult in installation, furthermore, disalignment is likely to be occurred in bad conditions and is likely to be damaged under high power, therefore, their availability is reduced.
In order to solve the above problems, a large amount of investigations have been made both at home and abroad. A red sapphire laser cavity consisted of a orientation prism and a plane output mirror was published in US Jemna Mechunika a optika No. 12 P.383-6 in 1968, while in patent U.S. Pat. No. 3,924,201, two right angle prisms (Paul prism) are used as two total reflective mirrors of the resonant cavity, in between the active material, Q-switch and an aside-output polarizer are located. The above two structures have partly solved the laser disalignment problem caused by vibration, temperature variation and so on. However, they only have the ability of avoiding misalignment and obtaining high stability in a special direction, while the installation and alignment are still difficult and they do not have the alignment-free characterisitics. A CN patent CN 87.8.16562 has provided a stably aligned, linearly polarized output laser, in which a corner prism is used as a reflector to form a folded optical resonant cavity. The total reflector and the output mirror of the cavity are formed by a glass plate coated with films of different reflectance in different area. In the cavity an optical alignment compensator is interpolated as an adjustable compensation for the optical path deviation caused by machinery errors of optical elements from optical axis. The optical resonant cavity can remain its alignment and have low misalignment even under a great temperature variation condition. Therefore, the laser can output a stabilized, Q-switched and linearly polarized high power laser beam. Problems of the cavity are that it has low disalignmentxe2x80x94resistance and is easy to be deformed under high power condition. Besides, since the corner prism is used only as a reflector, the regulation of the optical alignment compensator is technologically complicated, and it is not an alignment-free cavity. Now, the disalignment problem is usually solved by using a module assembled by adhesion and then solidification. However this module must be calibrated and fixed. Besides, this technology is complicated, and can be used only once, because it is hard to be repaired.
The object of the present invention is to overcome the problem of the conventional lasers that the cavity must be regulated by two sets of special means, and is to provide a simple structure, which can be stably operated after assemblage without alignment. This new structure has strong misalignmentxe2x80x94resistance, therefore, can provide a stable output laser beam of small divergence angle under strong vibration and large temperature variation environment.
The scheme of the present invention is as following:
The present invention provides an alignment-free solid laser, comprising an active material, a resonant cavity, a pump lamp, a pump power and a focusing cavity, characterized in that the active material is located in the focusing cavity, an orientation prism located in front of one end of the active material is used as a total reflector, the other end of the active material is coated with a transitivexe2x80x94reflective film and is used as a laser output mirror of the cavity, an applied voltage from the pump power is applied to the two ends of the pump lamp, the pump light is reflected and focused on the active material by the inner surfaces of the focusing cavity, the corner apex of the mentioned orientation prism is located on the axis of the active material to form the resonant cavity, the three total reflective inner surfaces of the corner apex of the orientation prism are perpendicular to one another, the shape of the orientation prism is equivalent to a corner cut from a cube and its bottom is of an equilateral triangle or circle shape;
The active material is an optical crystal which has been used in the conventional laser, such as red sapphire, Nd: glass, Nd: YAG, or the like;
The active material located in the focusing cavity can be one or more rods. When it consists of two rods, one rod with a total reflective film on one end and a transitive film on the other end is used as an oscillation rod, while the other rod with a transitive film on one end and a transitive-reflective film on the other end is used as an amplified rod. The two active material rods are symmetrically located relatively to the axis passed through the orientation prism corner apex to form a series alignment-free solid laser;
When the active material consists of many rods, the active material rod array is symmetrically distributed relatively to the axis passed through the corner apex of the orientation prism. One active material end closed to the orientation prism is coated with a transitive film, while the other end is coated with a transitive-reflective film and is used as an output mirror to form a high power solid laser with numbers of outputs, and without disalignment;
A Q-switch can also be put in the optical path between the active material end closed to the orientation prism and the orientation prism.
Comparing to the prior art, the present invention has the following advantages and effects:
1. The alignment-free solid laser according to the present invention uses an orientation prism as a total reflector. It can also use, for example, a Cr4+: YAG element as a Q-switch in the optical path, and uses one active material end with a transitive-reflective film as a output mirror to form a laser cavity. This laser has strong disalignment-resistance. The allowance of the disalignment angle of the orientation prism as a total reflector is up to xc2x120xc2x0, and the deviation of the prism central axis from the cavity axis is allowed up to D/4 (D is the diameter of the active material). It is impossible for the prior lasers to achieve such results. The technology of the present invention has overcome the problem of the laser failure caused by the laser cavity disalignment and therefore the laser can be operated normally after assemblage without alignment;
2. The orientation prism or total reflector of this laser has a feature of parallel reflection in principle. It can overcome the problem of the optical deformation caused by the refractance and gain nonhomogenity in the laser medium, heat-induced deformation, heat-induced birefractance etc. Therefore, the excellent performance of a uniform optical far-field, narrowed divergence angle and concentrated energy is achieved, and the laser beam quality is improved. The damage threshold of the laser crystal and Q-switch device can be reduced and the problem of the laser damage of the solid laser is solved better when the orientation prism or total reflector is used in a continuous or high repeated frequency Q-switched solid laser. Measurable distance, accuracy and angle resolution are increased when the orientation prism of total reflector is used in laser distance-measuring instruments;
3. This laser has a simple structure, reliable performance and is easy to be assembled. It makes various related lasers modified easily, is also of low cost. Furthermore, it is easy to be standardized and modularized to form solid lasers with different specifications, different parameters and for different purposes, therefore, can be extensively used in military, industrial processing, medical and scientific research fields.